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Structural analysis of bio-oils from pyrolysis and steam pyrolysis of cottonseed cake
Journal of Analytical and Applied Pyrolysis 60 (2001) 89 – 101 www.elsevier.com/locate/jaap
Structural analysis of bio-oils from pyrolysis and steam pyrolysis of cottonseed cake Nurgu¨l O8 zbay a, Ays¸e E. Pu¨tu¨n b,*, Ersan Pu¨tu¨n b b
a Anadolu Uni6ersity, Career School of Bozu¨yu¨k, Bilecik, Turkey Department of Chemical Engineering, Faculty of Engineering and Architecture, Anadolu Uni6ersity, I: ki Eylu¨l Campus, 26470, Eskis¸ehir, Turkey
Received 3 May 2000; accepted 18 September 2000
Abstract Structural analysis and the effect of the water vapour on the structure of the products obtained by low temperature thermal destruction of biomass at atmospheric pressure has been investigated. The liquid products were fractionated into pentane solubles and insolubles (Asphaltenes). Pentane solubles were then solvent fractionated into pentane, toluene, ether and methanol subfractions by fractionated column chromatograpy. The aliphatic subfractions of the oils were then analysed by capillary column gas-liquid chromatography and GC/MS. For further structural analysis, the pyrolysis oils and aromatic and polar subfractions were conducted using FTIR and 1H-NMR spectra. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Biomass; Cottonseed cake; Pyrolysis; Instrumental analysis
1. Introduction Contrary to the assumption that fossil fuels are the principal sources of fuels and organic chemicals, biomass in the last decade is recognised as a potential and important renewable source of energy and chemicals. Due to the negligible sulphur, nitrogen and metal content, the utilisation of biomass would mean recycling mobile carbon compared to the mobilisation of fixed carbon resulting from the combustion of fossil fuels [1]. * Corresponding author. Tel.: + 90-222-3223662; fax: + 90-222-3239501. E-mail address: [email protected] (A.E. Pu¨tu¨n). 0165-2370/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 5 - 2 3 7 0 ( 0 0 ) 0 0 1 6 1 - 3
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In the relevant literature a large number of plant species have been reported which are also capable of converting CO2 beyond carbohydrates to isoprenoids and other hydrocarbon-like compounds [2]. These biomass constituents can be used as starting materials in the production of transportation fuels and liquids obtained by thermal conversion have the advantage of the continuous supply of energy to countries without fossil fuel reserves and at times when petroleum supplies become scarce due to political or economical factors. Furthermore, usage of biomass may also help to minimise environmental problems while contributing to the world’s energy supply. Thermochemical processes are thought to have great promise as a means for converting biomass into higher value fuels. Pyrolysis lies at the heart of all the thermochemical fuel conversion processes and is assumed to become an avenue to petroleum-type products from renewable biomass. The economics for biomass pyrolysis are generally considered to be most favourable for (1) plants that grow abundantly and require little cultivation in and lands (2) wastes available in relatively large quantities from agricultural plants such as sunflower, hazelnut and cotton [3]. While interest in the pyrolysis of biomass has been increased, new technologies to increase the degree of conversion of solid fuels and biomass into liquid products has been developed. Amongst them, the method of steam pyrolysis is a special interest with the numerous advantages [4,5]. Steam can be absorbed on the surface of char and in this way inhibit the adsorption of tar vapours on char surface. This also prevents the secondary cracking reactions in the gas phase and helps to maximise the yield of liquid products. Cotton is one of the most important agricultural crops in Turkey, that is one of the eight countries that are providing 85% of the world’s cotton. Today, the cotton area is about 600 000 ha and gradually will increase to about 900 000 ha by 2002 with the completion of the GAP (Southeastern Anatolian Project) [6]. Although cotton is being cultivated mainly for its lint, which is universally used as a textile raw material, cottonseed oil industry generates cottonseed cake which can be considered as feedstock for future thermochemical demonstration unit [7]. The aim of this study is to report the effect of steam on the chemical composition of liquid hydrocarbons evolved from cottonseed cake and the relation of the composition with the process conditions.
2. Experimental The cottonseed cake sample investigated in this study has been taken from some cottonseed oil factories around Adana located in Southern Anatolia. The pyrolysis experiments were performed in two different atmospheres namely, static and water vapour in a Heinze reactor. The 316 stainless steel Heinze retort described previously [8–10] has a volume of 400 cm3 (70 mm ID) and is externally heated by an electrical furnace in which the temperature is measured by a thermocouple inside the bed. The connecting pipe
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between the reactor and the trapping system was heated to 400°C to avoid condensation of tar vapour. For the first part of pyrolysis experiments, 40 g sample of air-dried cake was placed into the reactor and the experiments were carried out with a temperature increment of 7 and 40 K min − 1 to the final temperatures of 400, 500, 550 and 700°C and the steam velocity of 0.6: 1.3: 2.7 cm s − 1. The liquid products were collected in a glass liner located in a cold trap maintained at 0°C. The liquid phase consisting of an aqueous and oil phase were separated and weighed. The total liquid product (oil+ water) was weighed in a dry-ice cooled trap and recovered in dichloromethylene for analysis. Water was determined by refluxing the toluene solution in a Dean– Stark apparatus. The bio-oils were then recovered from toluene solutions. The oils characterised in this study were the products of the optimum condition which were 550°C pyrolysis temperature, 7 K min − 1 heating rate and 1.3 cm s − 1 steam velocity only for steam pyrolysis.
2.1. Fractionation and characterisation of pyrolysis oils Both of the pyrolysis oils were separated into two fractions as pentane soluble and insoluble compounds (Asphaltenes) by 50 ml pentane. The pentane soluble materials were further separated on activated silica-gel (73– 230 mesh) pre-treated at 105°C for 2 h before being, introduced in a 20× 2.5 cm i.d column. 0.65 g of pyrolysis oil and 0.78 g of steam pyrolysis oil of pentane solubles were eluted with 150 ml pentane, 200 ml of toluene, ether and methanol to produce aliphatic, aromatic, esther and more polar fractions, respectively. Each fraction was dried and weighed and then subjected to elemental, GC and spectroscopic analyses. GC analysis with flame ionisation detection (FID) performed using a HewlettPackard 6890 Model Gas Chromatograph with nitrogen as the carrier gas and a thin film (30 m ×0.25 mm i.d.; 0.25 mm film thickness), HP-5MS capillary column supplied from Hewlett-Packard, USA. GC/MS analysis was carried out using a 6890 Model Gas Chromatography and a mass selective detector (Hewlett-Packard, USA). A thin film (30 m× 0.25 mm i.d.; 0.25 mm film thickness), HP-5MS capillary column supplied by Hewlett-Packard, USA was used. The mass spectrometer was set to scan for molecular masses ranging from 10 to 650 m total ion current (TIC) and selective ion monitoring to (SIM) modes. The FTIR spectroscopy of the bio-oils and pentane, toluene, ether and methanol subfractions were obtained on thin films between KBr plates by using a Jasco FT//IR 300 E Fourier Transform Infrared Spectrophotometer. 1 H-NMR spectra were recorded at 90 MHz using a Jeol EX 90A instrument for 20% wt. vol − 1 solutions in chloroform-d, containing TMS as an internal standard. Hydrogen distribution was combined with ultimate analyses and molecular masses to yield structural parameters by methods described elsewhere [11– 13].
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Table 1 Yields of static pyrolysis products at different temperatures (heating rate of 7 K min−1) Temperature (°C)
Conversion (%)
Oil (%)
Char (%)
400 500 550 700
72.18 73.57 73.55 76.49
22.67 24.07 24.47 21.90
27.82 26.43 26.45 23.51
3. Results and discussion
3.1. Bio-oil yields The yields of the static and steam pyrolysis are given in Tables 1 and 2. The results show that the oil yield of steam pyrolysis is higher than that of static pyrolysis.
3.2. Chemical composition The proximate analysis of cottonseed cake is given in Table 3. The elemental composition of static and steam pyrolysis oils are illustrated in Table 4. As can be seen from the tables, the bio-oils have low oxygen content and high H/C ratio than original feedstock. Comparison of H/C ratio with conventional fuels indicates that the H/C ratios of the oils obtained in this study lie between those of light and heavy petroleum products. Steam pyrolysed oil contains about two times less nitrogen (3%) than the other bio-oil (5.7%), whereas the amount of heteroatom oxygen in static oil (20.6%) is higher than in the steam atmosphere oil (13.5%). Both the oils were separated into two fractions as pentane soluble and insolubles. The yield of pentane solubles of the steam pyrolysis oil was higher (78%) than that of the static atmosphere (65%). The pentane soluble materials were further separated by adsorption chromatography. Overall results and yields of subfractions are presented in Table 5. In comparison to static retorting, the yields of aliphatics and aromatics increase markedly and polar compounds decrease slightly with the values of 20% aliphatic and 26% aromatic compounds when using steam as sweep gas. However, the Table 2 Yields of steam pyrolysis products with different flow rates at the optimum static pyrolysis temperature (heating rate of 7 K min−1, final temperature 550°C) Steam (cm sn−1)
Conversion (%)
Oil (%)
Char (%)
0.6 1.3 2.7
76.07 76.86 78.96
31.76 32.98 39.33
23.93 23.20 21.07
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Table 3 Analyses of cottonseed cake C (wt.%) H (wt.%) N (wt.%) O (wt.%)a Ash (wt.%, dry basis) Moisture (wt.%, as received) Volatile matter(wt.%, daf) Fixed carbon (wt.% daf) Raw cellulose (wt.% daf) Calorific value (Kcal kg−1) a
52.0 5.9 1.3 40.8 6.1 4.9 78.7 10.3 27.24 4300
By difference.
aliphatic and aromatic fractions of static oil were 11 and 23%, respectively. From these results one can say that steam pyrolysis is found to be more suitable for the production of hydrocarbons.
3.3. Oil functional group composition Fig. 1 shows the Fourier transform infrared (FTIR) spectra, representing functional group compositional analysis of both pyrolysis oils and subfractions of the pentane soluble materials. The results are summarised in Table 6. The OH stretching vibrations between 3300 and 3600 cm − 1 of the bio-oils and the polar subfractions, namely ether and methanol, indicate the presence of phenols and alcohols. In addition the presence of these peaks together with CC stretching vibrations between 1680 and 1700 cm − 1 is compatible with the presence of ketone, quinone, aldehyde groups etc [14]. The presence of alkane groups in pyrolysis oil derived from biomass was indicated by the CH bending vibrations between 1380 and 1465 cm − 1. Moreover, the location of bending vibration of CH3 groups at 1390 cm − 1 can be given as an other evidence since this band is very important for the detection of methyl groups in a given compound. The CH stretching vibrations Table 4 Elemental composition static and steam pyrolysis
C (wt.%) H (wt.%) N (wt.%) O (wt.%)a Atomic H/C ratio Atomic O/C ratio a
By difference.
Static pyrolysis
Steam pyrolysis
65.9 8.5 5.7 19.9 1.55 0.19
73.98 9.65 3.05 13.32 1.56 0.13
a
10.6
65.0
By difference.
Yield (wt.%, bio-oil basis) C (wt.%) H (wt.%) N (wt.%) 0 (wt.%)a Atomic H/C ratio Atomic OIC ratio
Ether eluate
23.0
76.6 9.4 2.1 14.1 1.48 0.12
11.0
76.8 12.6 – 11.9 1.96 0.10
0.14
73.7 10.6 L.6 15.5 1.73
40.0
0.15
1.64
67.5 9.2 7.8
26.0
78.1
MeOH eluate Total
Toluene eluate
Total
Pentane eluate
Steam
Static
Pentane soluble materials
Table 5 Yields and analyses for the fractionated bio-oil static and steam pyrolysis
0.07
80.4 11.9 – 7.6 1.79
18.8
Pentane eluate
0.10
77.5 11.6 0.21 10.7 1.80
25.0
Toluene eluate
0.14
74A 10.5 1.01 13.9 1.72
43.7
Ether eluate
0.16
69.1 8.65 5.9 16.2 1.50
12.5
MeOH eluate
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3600–3200 + 2960–2926 2900–2870 1718–1680 1645 1610, 1500, 1420 1465, 1380 1460–1450 1270–1060 1390 1240 1120 1100 1080–1025 700–900 − 720–725 698
OH stretch Aromatic ring stretching wasa wsb Carbonyl CC stretch Aromatic CC stretch l sc lasd CO stretch CH3 bending OH bending Ketone or ester bending Polycyclic heteroatms In plane CH bending Substituents of in aromatic ring Out of plane CH bending Rocking band e Out of planeCH bending
b
c
Ether
Methanol
+ − + + + 9 + + + + + − − − − − − + −
− +− + + − + − + + − + − − − − − + + −
+ + − − + − + + − + + − − − + + + − +
+ + + + + − − + + + + + + − − − − − +
+ − − − + − − + − + + − − + − + − − −
+ + + + + − − + + + + − − − − − − + −
Bio-oil
Toluene
Bio-oil
Pentane
Steam
Static
Asymmetrical CH stretching vibration of aliphatic CH3 and CH2. Symmetrical CH stretching vibration of aliphatic CH3 and CH2. Scissoring bending vibration of aliphatic CH2. d Asymmetrical CH bending vibration of aliphatic CH3. e C7\carbon atoms.
a
Wavenumber (cm−1)
Type of functional group
Table 6 Results of FIFIR for original and subfractions of two bio-oils from the fixed-bed pyrolysis of cottonseedcake
− − + + − − − + + − + − − − − − + + −
Pentane + − − − + − + + − − + − − − + + + − +
Toluene
− + + − − + + + + + + − − − − − +
+
Ether
− −
− + + − − + − + + − − + − +
Methanol
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Fig. 1. IR spectra of fractions separated from the bio-oil from the fixed-bed pyrolysis of cottonseed cake. (a) Bio-oil from static; (b) bio-oil from water vapour; (c) pentane subfraction from static; (d) pentane subfraction from water vapour; (e) toluene subfraction from static; (f) toluene subfraction from water vapour; (g) ether subfraction from static; (h) ether subfraction from water vapour; (i) methanol subfraction from static; (j) methanol subfraction from water vapour.
of aliphatic bonding to the aromatic ring at 2900 and 2960 cm − 1 are important evidence of the aromaticity of toluene subfraction. According to some earlier work single ring aromatic and alkylated aromatic compounds such as benzene, toluene and polycyclic aromatic compounds were identified in biomass-derived pyrolysis oils [14,15]. Indeed absorption peaks between 698–900 and 1420–1610 cm − 1 indicate mono and polycylic and substituted aromatic groups.
3.4. 1H-NMR based structural analyses 1
H-NMR spectra were applied to both the oils and toluene, ether and methanol subfractions and the results are summarised in Fig. 2. The hydrogen distribution of 1 H-NMR is given in Table 7. 1H-NMR spectra of the bio-oils are indicated that the aromaticity of the bio-oil of steam pyrolysis was higher than the other bio-oil (5.5 vs. 3.0%). When considering the aromatic character of the subfraction of the oil from steam pyrolysis, an increase can be seen in the aromatic character of the methanol subfraction compared to the others, due to the high molecular weight polycyclic aromatic compounds and phenolic OH groups. Aromatic ring joining methylene protons called HF, are dominant in the bio-oil of steam pyrolysis and are indicated by a characteristic peak in the range of 3.5–4.5 ppm. The protons in the a position to an aromatic ring were also observed in both oils and their subfractions but in different amounts. i- CH3, CH2 and CH k or further from an aromatic ring proton (centred at 1.25 ppm) of the oils and their subfractions are higher than the other protons. They are related to the aliphatic chain bonded to the aromatic ring. CH3 k or further from an aromatic ring protons are also observed and all of these protons are in very close amounts in the oils and their subfractions except the methanol subfraction of the steam pyrolysis oil [16,17].
2.95 1.72 1.29 19.66 4.40 63.85 10.53
6.5–9.0 5.0–6.5 3.3–4.5 2.0–3.3 1.6–2.0 1.0–1.6 0.5–1.0
Aromatic Phenolic (OH) or olefinic proton Ring-joinmethylene (ArCH2Ar) CH3. CH2 and CH to an aromatic ring CH2 and CH b to an aromatic ring (napthenic) b-CH3, CH2 and CH g or further from an aromatic ring CH3 g or further from an aromatic ring 11.35
61.57
7.68 2.55 4.54 12.31 –
8.42
67.21
3.94 2.90 2.90 9.92 4.71
7.10
48.26
34.54 2.13 – 7.97 –
Methanol
9.63
65.69
5.45 3.17 1.59 8.25 6.22
8.90
78.65
0.75 3.01 – 8.69 –
Toluene
Bio-oil
Ether
Bio-oil
Toluene
Bio-oil steam
Bio-oil static
Chemical shift (ppm)
Type of hydrogen
9.59
66.91
2.84 4.52 2.90 7.76 5.48
Ether
4.83
36.01
41.06 2.68 2.14 6.69 6.58
Methanol
Table 7 Results of 1H-NMR for original and subfractions (toluene, ether, methanol) of two bio-oils from the fixed-bed pyrolysis of cottonseed cake (percentage hydrogen total)
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3.5. GC and GC/MS analyses of the pentane eluate Gas liquid chromatograms of the aliphatic subfractions of pentane soluble compounds of both bio-oils are illustrated in Fig. 3.
Fig. 2. 1H-NMR spectra of fractions separated from the bio-oil from the fixed-bed pyrolysis of cottonseed cake. (a) Bio-oil from static; (b) bio-oil from water vapour; (c) toluene subfraction from static; (d) toluene subfraction from water vapour; (e) ether subfraction from static; (f) ether subfraction from water vapour; (g) methanol subfraction from static; (h) methanol subfraction from water vapour.
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The hydrocarbons were identified by gas chromatography using external standards. Three types of compounds were identified in pentane subfractions: normal alkanes, alkenes, and branched hyrdocarbons (isoprenoids). The ranges of the straight-chain alkanes were C10 – C32 and C12 –C32 in the steam and static oils, respectively. This suggests that the oils produced under water vapour have a
Fig. 3. GC analysis of pentane subfraction the bio-oil from cotton seed cake using a thin film (30 m× 0.25 min i.d.; 0.25 mm film thickness) HP-5MS capillary column. (a) Pentane subfraction from static; (b) pentane subfraction from water vapour, Pri, Pristane, Npr, Norpristane, Pri, Pristene, Ph, Phytane.
100
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relatively large fraction of lighter hydrocarbons. The most abundant n-alkane distribution was observed in the range of C12 –C22 in both of the oils but peak intensity was different. Due to indirect hydrogen introduction to the retort, the peak intensity of the pentane subfraction of steam pyrolysis oil was higher than the pentane subfraction of static retorting oil. Thus according to the GC analysis it can be concluded that the compounds which are obtained during the process of steam pyrolysis are predominantly saturated structures probably due to the conversion of unsaturated hydrocarbons(alkenes) to saturated hydrocarbons(alkanes) while the desorption of low molecular products take place. This is also consistent with the results obtained for the lignites and oil shales [10–18]. 1H-NMR and IR spectra of the oils corroborated this result, as well. The isoprenoid (branched hydrocarbons) alkanes are most abundant compounds in the branched/cyclic alkane fraction. Four isoprenoid hydrocarbons, namely norpristane (Npr), pristane (Pr), pristene (Pri) and phytene (Ph) were identified in pentane subfraction of both oils. This is consistent with the detection of C16 C17 and C18 skeletons in the pyrolysis oils of oil shales [18,19]. GC/MS analyses were conducted on the pentane subfractions to confirm nalkane and n-alkene hydrocarbons (Fig. 4). Compounds containing more than eight
Fig. 4. Chromatogram of the pentane subfraction of the bio-oil from cottonseed cake run on the GC/MS system. The number on the peaks in the centre selected ion current chromatograms (m/e= 57, 55) indicate the chain length of n-alkanes and alkenes.
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atoms show fairly similar chromatograms; identification then was hand in the molecular ion peak. Reconstructed selected ion current chromatogram for the alkanes (m/e = 57) and alkenes (m/e= 55) are also shown in Fig. 4. 4. Conclusion The effect of steam on the pyrolysis of biomass more pronounced with a significant increase in oil yield. As it is consistent with the literature, steam inhibits the secondary cracking reactions of the products of pyrolysis. In addition, the oils are more paraffinic than those obtained by static retorting. Furthermore the role of steam flow rate needs some detailed studies on the characterisation of bio-oils because of the possibility of increasing the amounts of paraffinic and aromatic compounds. As considering this study one can say that, the spectroscopic results are consistent with the chromatographic data, confirming that the hydrocarbons of the pentane subfractions of both pyrolysis oils are mixtures of alkanes and alkenes. Comparison of H/C ratios with conventional fuels has shown that the H/C ratios of the oils obtained in this work is between those of light and heavy petroleum products. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
R.K. Sharma, N.N. Bakshi, Bioresour. Technol. 45 (1993) 195 – 203. E.K. Nemethy, J.W. Otvos, M. Calvin, Pure Appl. Chem. 53 (1981) 1101 – 1108. A.E. Pu¨ tu¨ n, N. O8 zbay, O8 .M. Koc¸ kar, E. Pu¨ tu¨ n, Energy Sour. 19 (1997) 9. K. Alharfi, A. Mokhlisse, M.B Chanca, J. Anal. Appl. Pyrol. 48 (1999) 65 – 76. V. Minkova, M. Razvigorava, M. Goronava, L. Ljutzkanov, G. Angelova, Fuel 70 (1991) 713 – 719. M.H. Eisa, S. Barghouti, F. Gillham, M. T. Alsaffaty, World bank technical paper 201, (1994) 112. E. Pu¨ tu¨ n, O8 .M. Koc¸ kar, F. Gerc¸ el, S. Brown, J. Andresen, C. McRae, C.E. Snape, World Renewable Energy Congress 5 (1994a) 816 – 818. R. Heinze., 1943. Oel u Kohle, 39, 973. E. Pu¨ tu¨ n, S. Bes¸ler, A.E. Pu¨ tu¨ n, E. Ekinci, Chim. Acta Turcica 17 (1989) 307. E. Ekinci, M. C ¸ itirog˘ lu, E. Pu¨ tu¨ n, G.D. Love, C.J. Lafferty, C.E. Snape, Fuel 71 (1992) 1511 – 1515. A.E. Pu¨ tu¨ n, O8 .M. Koc¸ kar, S. Yorgun, H.F. Gerc¸ el, J. Andresen, C.E. Snape, E. Pu¨ tu¨ n, Fuel Process Technol. 46 (1) (1996) 49 –62. A.E. Pu¨ tu¨ n, H.F. Gerc¸ el, O8 .M. Koc¸ kar, O. Ege, C.E. Snape, E. Pu¨ tu¨ n, Fuel 75 (11) (1996) 1307 – 1312. A.E. Pu¨ tu¨ n, A. O8 zcan, E. Pu¨ tu¨ n, J. Anal. Appl. Pyrol. 52 (1999) 33 – 49. P.L. Desbene, M. Essayegh, B. Desmazieres, J.J. Basselier, in: A.V. Bridgwater, G. Grassi (Eds.), Biomass Pyrolysis Liquids, Upgrading and Utilisation, Elsevier, London, 1991. D.C. Elliott, in: E.J. Soltes, T.A. Milne (Eds.), Pyrolysis Oils from Biomass, Producing, Analysing and Upgrading, ACS Symposium Series 376, Washington, DC, 1988. Z.J. Stompel, K.D. Bartle, Fuel 62 (1983) 900. N. O8 zbay, Pyrolysis of cotton seed cake and characterization of the liquid products, Ph. D. thesis, Osmangazi University, Eskis¸ehir, 1998. M. Razvigorova, M. Goranova, V. Minkova, N. Russyanavo, Fuel 74 (1995) 1333. K.D. Bartle, D.W. Jones, H. Pakdel, Analytical Methods for Coal and Coal Products, Academic Press, New York, 1978, p. 223.
Structural analysis of bio-oils from pyrolysis and steam pyrolysis of cottonseed cake Nurgu¨l O8 zbay a, Ays¸e E. Pu¨tu¨n b,*, Ersan Pu¨tu¨n b b
a Anadolu Uni6ersity, Career School of Bozu¨yu¨k, Bilecik, Turkey Department of Chemical Engineering, Faculty of Engineering and Architecture, Anadolu Uni6ersity, I: ki Eylu¨l Campus, 26470, Eskis¸ehir, Turkey
Received 3 May 2000; accepted 18 September 2000
Abstract Structural analysis and the effect of the water vapour on the structure of the products obtained by low temperature thermal destruction of biomass at atmospheric pressure has been investigated. The liquid products were fractionated into pentane solubles and insolubles (Asphaltenes). Pentane solubles were then solvent fractionated into pentane, toluene, ether and methanol subfractions by fractionated column chromatograpy. The aliphatic subfractions of the oils were then analysed by capillary column gas-liquid chromatography and GC/MS. For further structural analysis, the pyrolysis oils and aromatic and polar subfractions were conducted using FTIR and 1H-NMR spectra. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Biomass; Cottonseed cake; Pyrolysis; Instrumental analysis
1. Introduction Contrary to the assumption that fossil fuels are the principal sources of fuels and organic chemicals, biomass in the last decade is recognised as a potential and important renewable source of energy and chemicals. Due to the negligible sulphur, nitrogen and metal content, the utilisation of biomass would mean recycling mobile carbon compared to the mobilisation of fixed carbon resulting from the combustion of fossil fuels [1]. * Corresponding author. Tel.: + 90-222-3223662; fax: + 90-222-3239501. E-mail address: [email protected] (A.E. Pu¨tu¨n). 0165-2370/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 5 - 2 3 7 0 ( 0 0 ) 0 0 1 6 1 - 3
90
N. O8 zbay et al. / J. Anal. Appl. Pyrolysis 60 (2001) 89–101
In the relevant literature a large number of plant species have been reported which are also capable of converting CO2 beyond carbohydrates to isoprenoids and other hydrocarbon-like compounds [2]. These biomass constituents can be used as starting materials in the production of transportation fuels and liquids obtained by thermal conversion have the advantage of the continuous supply of energy to countries without fossil fuel reserves and at times when petroleum supplies become scarce due to political or economical factors. Furthermore, usage of biomass may also help to minimise environmental problems while contributing to the world’s energy supply. Thermochemical processes are thought to have great promise as a means for converting biomass into higher value fuels. Pyrolysis lies at the heart of all the thermochemical fuel conversion processes and is assumed to become an avenue to petroleum-type products from renewable biomass. The economics for biomass pyrolysis are generally considered to be most favourable for (1) plants that grow abundantly and require little cultivation in and lands (2) wastes available in relatively large quantities from agricultural plants such as sunflower, hazelnut and cotton [3]. While interest in the pyrolysis of biomass has been increased, new technologies to increase the degree of conversion of solid fuels and biomass into liquid products has been developed. Amongst them, the method of steam pyrolysis is a special interest with the numerous advantages [4,5]. Steam can be absorbed on the surface of char and in this way inhibit the adsorption of tar vapours on char surface. This also prevents the secondary cracking reactions in the gas phase and helps to maximise the yield of liquid products. Cotton is one of the most important agricultural crops in Turkey, that is one of the eight countries that are providing 85% of the world’s cotton. Today, the cotton area is about 600 000 ha and gradually will increase to about 900 000 ha by 2002 with the completion of the GAP (Southeastern Anatolian Project) [6]. Although cotton is being cultivated mainly for its lint, which is universally used as a textile raw material, cottonseed oil industry generates cottonseed cake which can be considered as feedstock for future thermochemical demonstration unit [7]. The aim of this study is to report the effect of steam on the chemical composition of liquid hydrocarbons evolved from cottonseed cake and the relation of the composition with the process conditions.
2. Experimental The cottonseed cake sample investigated in this study has been taken from some cottonseed oil factories around Adana located in Southern Anatolia. The pyrolysis experiments were performed in two different atmospheres namely, static and water vapour in a Heinze reactor. The 316 stainless steel Heinze retort described previously [8–10] has a volume of 400 cm3 (70 mm ID) and is externally heated by an electrical furnace in which the temperature is measured by a thermocouple inside the bed. The connecting pipe
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between the reactor and the trapping system was heated to 400°C to avoid condensation of tar vapour. For the first part of pyrolysis experiments, 40 g sample of air-dried cake was placed into the reactor and the experiments were carried out with a temperature increment of 7 and 40 K min − 1 to the final temperatures of 400, 500, 550 and 700°C and the steam velocity of 0.6: 1.3: 2.7 cm s − 1. The liquid products were collected in a glass liner located in a cold trap maintained at 0°C. The liquid phase consisting of an aqueous and oil phase were separated and weighed. The total liquid product (oil+ water) was weighed in a dry-ice cooled trap and recovered in dichloromethylene for analysis. Water was determined by refluxing the toluene solution in a Dean– Stark apparatus. The bio-oils were then recovered from toluene solutions. The oils characterised in this study were the products of the optimum condition which were 550°C pyrolysis temperature, 7 K min − 1 heating rate and 1.3 cm s − 1 steam velocity only for steam pyrolysis.
2.1. Fractionation and characterisation of pyrolysis oils Both of the pyrolysis oils were separated into two fractions as pentane soluble and insoluble compounds (Asphaltenes) by 50 ml pentane. The pentane soluble materials were further separated on activated silica-gel (73– 230 mesh) pre-treated at 105°C for 2 h before being, introduced in a 20× 2.5 cm i.d column. 0.65 g of pyrolysis oil and 0.78 g of steam pyrolysis oil of pentane solubles were eluted with 150 ml pentane, 200 ml of toluene, ether and methanol to produce aliphatic, aromatic, esther and more polar fractions, respectively. Each fraction was dried and weighed and then subjected to elemental, GC and spectroscopic analyses. GC analysis with flame ionisation detection (FID) performed using a HewlettPackard 6890 Model Gas Chromatograph with nitrogen as the carrier gas and a thin film (30 m ×0.25 mm i.d.; 0.25 mm film thickness), HP-5MS capillary column supplied from Hewlett-Packard, USA. GC/MS analysis was carried out using a 6890 Model Gas Chromatography and a mass selective detector (Hewlett-Packard, USA). A thin film (30 m× 0.25 mm i.d.; 0.25 mm film thickness), HP-5MS capillary column supplied by Hewlett-Packard, USA was used. The mass spectrometer was set to scan for molecular masses ranging from 10 to 650 m total ion current (TIC) and selective ion monitoring to (SIM) modes. The FTIR spectroscopy of the bio-oils and pentane, toluene, ether and methanol subfractions were obtained on thin films between KBr plates by using a Jasco FT//IR 300 E Fourier Transform Infrared Spectrophotometer. 1 H-NMR spectra were recorded at 90 MHz using a Jeol EX 90A instrument for 20% wt. vol − 1 solutions in chloroform-d, containing TMS as an internal standard. Hydrogen distribution was combined with ultimate analyses and molecular masses to yield structural parameters by methods described elsewhere [11– 13].
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Table 1 Yields of static pyrolysis products at different temperatures (heating rate of 7 K min−1) Temperature (°C)
Conversion (%)
Oil (%)
Char (%)
400 500 550 700
72.18 73.57 73.55 76.49
22.67 24.07 24.47 21.90
27.82 26.43 26.45 23.51
3. Results and discussion
3.1. Bio-oil yields The yields of the static and steam pyrolysis are given in Tables 1 and 2. The results show that the oil yield of steam pyrolysis is higher than that of static pyrolysis.
3.2. Chemical composition The proximate analysis of cottonseed cake is given in Table 3. The elemental composition of static and steam pyrolysis oils are illustrated in Table 4. As can be seen from the tables, the bio-oils have low oxygen content and high H/C ratio than original feedstock. Comparison of H/C ratio with conventional fuels indicates that the H/C ratios of the oils obtained in this study lie between those of light and heavy petroleum products. Steam pyrolysed oil contains about two times less nitrogen (3%) than the other bio-oil (5.7%), whereas the amount of heteroatom oxygen in static oil (20.6%) is higher than in the steam atmosphere oil (13.5%). Both the oils were separated into two fractions as pentane soluble and insolubles. The yield of pentane solubles of the steam pyrolysis oil was higher (78%) than that of the static atmosphere (65%). The pentane soluble materials were further separated by adsorption chromatography. Overall results and yields of subfractions are presented in Table 5. In comparison to static retorting, the yields of aliphatics and aromatics increase markedly and polar compounds decrease slightly with the values of 20% aliphatic and 26% aromatic compounds when using steam as sweep gas. However, the Table 2 Yields of steam pyrolysis products with different flow rates at the optimum static pyrolysis temperature (heating rate of 7 K min−1, final temperature 550°C) Steam (cm sn−1)
Conversion (%)
Oil (%)
Char (%)
0.6 1.3 2.7
76.07 76.86 78.96
31.76 32.98 39.33
23.93 23.20 21.07
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Table 3 Analyses of cottonseed cake C (wt.%) H (wt.%) N (wt.%) O (wt.%)a Ash (wt.%, dry basis) Moisture (wt.%, as received) Volatile matter(wt.%, daf) Fixed carbon (wt.% daf) Raw cellulose (wt.% daf) Calorific value (Kcal kg−1) a
52.0 5.9 1.3 40.8 6.1 4.9 78.7 10.3 27.24 4300
By difference.
aliphatic and aromatic fractions of static oil were 11 and 23%, respectively. From these results one can say that steam pyrolysis is found to be more suitable for the production of hydrocarbons.
3.3. Oil functional group composition Fig. 1 shows the Fourier transform infrared (FTIR) spectra, representing functional group compositional analysis of both pyrolysis oils and subfractions of the pentane soluble materials. The results are summarised in Table 6. The OH stretching vibrations between 3300 and 3600 cm − 1 of the bio-oils and the polar subfractions, namely ether and methanol, indicate the presence of phenols and alcohols. In addition the presence of these peaks together with CC stretching vibrations between 1680 and 1700 cm − 1 is compatible with the presence of ketone, quinone, aldehyde groups etc [14]. The presence of alkane groups in pyrolysis oil derived from biomass was indicated by the CH bending vibrations between 1380 and 1465 cm − 1. Moreover, the location of bending vibration of CH3 groups at 1390 cm − 1 can be given as an other evidence since this band is very important for the detection of methyl groups in a given compound. The CH stretching vibrations Table 4 Elemental composition static and steam pyrolysis
C (wt.%) H (wt.%) N (wt.%) O (wt.%)a Atomic H/C ratio Atomic O/C ratio a
By difference.
Static pyrolysis
Steam pyrolysis
65.9 8.5 5.7 19.9 1.55 0.19
73.98 9.65 3.05 13.32 1.56 0.13
a
10.6
65.0
By difference.
Yield (wt.%, bio-oil basis) C (wt.%) H (wt.%) N (wt.%) 0 (wt.%)a Atomic H/C ratio Atomic OIC ratio
Ether eluate
23.0
76.6 9.4 2.1 14.1 1.48 0.12
11.0
76.8 12.6 – 11.9 1.96 0.10
0.14
73.7 10.6 L.6 15.5 1.73
40.0
0.15
1.64
67.5 9.2 7.8
26.0
78.1
MeOH eluate Total
Toluene eluate
Total
Pentane eluate
Steam
Static
Pentane soluble materials
Table 5 Yields and analyses for the fractionated bio-oil static and steam pyrolysis
0.07
80.4 11.9 – 7.6 1.79
18.8
Pentane eluate
0.10
77.5 11.6 0.21 10.7 1.80
25.0
Toluene eluate
0.14
74A 10.5 1.01 13.9 1.72
43.7
Ether eluate
0.16
69.1 8.65 5.9 16.2 1.50
12.5
MeOH eluate
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3600–3200 + 2960–2926 2900–2870 1718–1680 1645 1610, 1500, 1420 1465, 1380 1460–1450 1270–1060 1390 1240 1120 1100 1080–1025 700–900 − 720–725 698
OH stretch Aromatic ring stretching wasa wsb Carbonyl CC stretch Aromatic CC stretch l sc lasd CO stretch CH3 bending OH bending Ketone or ester bending Polycyclic heteroatms In plane CH bending Substituents of in aromatic ring Out of plane CH bending Rocking band e Out of planeCH bending
b
c
Ether
Methanol
+ − + + + 9 + + + + + − − − − − − + −
− +− + + − + − + + − + − − − − − + + −
+ + − − + − + + − + + − − − + + + − +
+ + + + + − − + + + + + + − − − − − +
+ − − − + − − + − + + − − + − + − − −
+ + + + + − − + + + + − − − − − − + −
Bio-oil
Toluene
Bio-oil
Pentane
Steam
Static
Asymmetrical CH stretching vibration of aliphatic CH3 and CH2. Symmetrical CH stretching vibration of aliphatic CH3 and CH2. Scissoring bending vibration of aliphatic CH2. d Asymmetrical CH bending vibration of aliphatic CH3. e C7\carbon atoms.
a
Wavenumber (cm−1)
Type of functional group
Table 6 Results of FIFIR for original and subfractions of two bio-oils from the fixed-bed pyrolysis of cottonseedcake
− − + + − − − + + − + − − − − − + + −
Pentane + − − − + − + + − − + − − − + + + − +
Toluene
− + + − − + + + + + + − − − − − +
+
Ether
− −
− + + − − + − + + − − + − +
Methanol
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Fig. 1. IR spectra of fractions separated from the bio-oil from the fixed-bed pyrolysis of cottonseed cake. (a) Bio-oil from static; (b) bio-oil from water vapour; (c) pentane subfraction from static; (d) pentane subfraction from water vapour; (e) toluene subfraction from static; (f) toluene subfraction from water vapour; (g) ether subfraction from static; (h) ether subfraction from water vapour; (i) methanol subfraction from static; (j) methanol subfraction from water vapour.
of aliphatic bonding to the aromatic ring at 2900 and 2960 cm − 1 are important evidence of the aromaticity of toluene subfraction. According to some earlier work single ring aromatic and alkylated aromatic compounds such as benzene, toluene and polycyclic aromatic compounds were identified in biomass-derived pyrolysis oils [14,15]. Indeed absorption peaks between 698–900 and 1420–1610 cm − 1 indicate mono and polycylic and substituted aromatic groups.
3.4. 1H-NMR based structural analyses 1
H-NMR spectra were applied to both the oils and toluene, ether and methanol subfractions and the results are summarised in Fig. 2. The hydrogen distribution of 1 H-NMR is given in Table 7. 1H-NMR spectra of the bio-oils are indicated that the aromaticity of the bio-oil of steam pyrolysis was higher than the other bio-oil (5.5 vs. 3.0%). When considering the aromatic character of the subfraction of the oil from steam pyrolysis, an increase can be seen in the aromatic character of the methanol subfraction compared to the others, due to the high molecular weight polycyclic aromatic compounds and phenolic OH groups. Aromatic ring joining methylene protons called HF, are dominant in the bio-oil of steam pyrolysis and are indicated by a characteristic peak in the range of 3.5–4.5 ppm. The protons in the a position to an aromatic ring were also observed in both oils and their subfractions but in different amounts. i- CH3, CH2 and CH k or further from an aromatic ring proton (centred at 1.25 ppm) of the oils and their subfractions are higher than the other protons. They are related to the aliphatic chain bonded to the aromatic ring. CH3 k or further from an aromatic ring protons are also observed and all of these protons are in very close amounts in the oils and their subfractions except the methanol subfraction of the steam pyrolysis oil [16,17].
2.95 1.72 1.29 19.66 4.40 63.85 10.53
6.5–9.0 5.0–6.5 3.3–4.5 2.0–3.3 1.6–2.0 1.0–1.6 0.5–1.0
Aromatic Phenolic (OH) or olefinic proton Ring-joinmethylene (ArCH2Ar) CH3. CH2 and CH to an aromatic ring CH2 and CH b to an aromatic ring (napthenic) b-CH3, CH2 and CH g or further from an aromatic ring CH3 g or further from an aromatic ring 11.35
61.57
7.68 2.55 4.54 12.31 –
8.42
67.21
3.94 2.90 2.90 9.92 4.71
7.10
48.26
34.54 2.13 – 7.97 –
Methanol
9.63
65.69
5.45 3.17 1.59 8.25 6.22
8.90
78.65
0.75 3.01 – 8.69 –
Toluene
Bio-oil
Ether
Bio-oil
Toluene
Bio-oil steam
Bio-oil static
Chemical shift (ppm)
Type of hydrogen
9.59
66.91
2.84 4.52 2.90 7.76 5.48
Ether
4.83
36.01
41.06 2.68 2.14 6.69 6.58
Methanol
Table 7 Results of 1H-NMR for original and subfractions (toluene, ether, methanol) of two bio-oils from the fixed-bed pyrolysis of cottonseed cake (percentage hydrogen total)
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3.5. GC and GC/MS analyses of the pentane eluate Gas liquid chromatograms of the aliphatic subfractions of pentane soluble compounds of both bio-oils are illustrated in Fig. 3.
Fig. 2. 1H-NMR spectra of fractions separated from the bio-oil from the fixed-bed pyrolysis of cottonseed cake. (a) Bio-oil from static; (b) bio-oil from water vapour; (c) toluene subfraction from static; (d) toluene subfraction from water vapour; (e) ether subfraction from static; (f) ether subfraction from water vapour; (g) methanol subfraction from static; (h) methanol subfraction from water vapour.
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The hydrocarbons were identified by gas chromatography using external standards. Three types of compounds were identified in pentane subfractions: normal alkanes, alkenes, and branched hyrdocarbons (isoprenoids). The ranges of the straight-chain alkanes were C10 – C32 and C12 –C32 in the steam and static oils, respectively. This suggests that the oils produced under water vapour have a
Fig. 3. GC analysis of pentane subfraction the bio-oil from cotton seed cake using a thin film (30 m× 0.25 min i.d.; 0.25 mm film thickness) HP-5MS capillary column. (a) Pentane subfraction from static; (b) pentane subfraction from water vapour, Pri, Pristane, Npr, Norpristane, Pri, Pristene, Ph, Phytane.
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relatively large fraction of lighter hydrocarbons. The most abundant n-alkane distribution was observed in the range of C12 –C22 in both of the oils but peak intensity was different. Due to indirect hydrogen introduction to the retort, the peak intensity of the pentane subfraction of steam pyrolysis oil was higher than the pentane subfraction of static retorting oil. Thus according to the GC analysis it can be concluded that the compounds which are obtained during the process of steam pyrolysis are predominantly saturated structures probably due to the conversion of unsaturated hydrocarbons(alkenes) to saturated hydrocarbons(alkanes) while the desorption of low molecular products take place. This is also consistent with the results obtained for the lignites and oil shales [10–18]. 1H-NMR and IR spectra of the oils corroborated this result, as well. The isoprenoid (branched hydrocarbons) alkanes are most abundant compounds in the branched/cyclic alkane fraction. Four isoprenoid hydrocarbons, namely norpristane (Npr), pristane (Pr), pristene (Pri) and phytene (Ph) were identified in pentane subfraction of both oils. This is consistent with the detection of C16 C17 and C18 skeletons in the pyrolysis oils of oil shales [18,19]. GC/MS analyses were conducted on the pentane subfractions to confirm nalkane and n-alkene hydrocarbons (Fig. 4). Compounds containing more than eight
Fig. 4. Chromatogram of the pentane subfraction of the bio-oil from cottonseed cake run on the GC/MS system. The number on the peaks in the centre selected ion current chromatograms (m/e= 57, 55) indicate the chain length of n-alkanes and alkenes.
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atoms show fairly similar chromatograms; identification then was hand in the molecular ion peak. Reconstructed selected ion current chromatogram for the alkanes (m/e = 57) and alkenes (m/e= 55) are also shown in Fig. 4. 4. Conclusion The effect of steam on the pyrolysis of biomass more pronounced with a significant increase in oil yield. As it is consistent with the literature, steam inhibits the secondary cracking reactions of the products of pyrolysis. In addition, the oils are more paraffinic than those obtained by static retorting. Furthermore the role of steam flow rate needs some detailed studies on the characterisation of bio-oils because of the possibility of increasing the amounts of paraffinic and aromatic compounds. As considering this study one can say that, the spectroscopic results are consistent with the chromatographic data, confirming that the hydrocarbons of the pentane subfractions of both pyrolysis oils are mixtures of alkanes and alkenes. Comparison of H/C ratios with conventional fuels has shown that the H/C ratios of the oils obtained in this work is between those of light and heavy petroleum products. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
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